That and a bunch of rust!
Got to get the gear/belt housing tapped/ pried off it. You spraying with loose juice?
Heat is your friend here. Keep it spread out and heat the whole circumference of the mount the starter is stuck in and tap back on starter .........It will come out.
Second cc's advice. I put cold packs on the motor and heated the entire periphery of the bracket and gently tapped here and there. Once it moved a fraction, the rest was easy. It just has to move a little, and then you can magnify that movement without going to town on it. Once out and cleaned up with sandpaper, apply copper antiseize